Continuous degree of freedom acoustic cores

ABSTRACT

An acoustic liner and a method of attenuating noise are provided. The acoustic liner includes a face sheet, a back sheet spaced from the face sheet, and a core layer extending between the face sheet and the back sheet. The core layer includes a plurality of resonant cells, each resonant cell including at least one cell wall coupled to the back sheet along a cell wall base edge. The at least one cell wall extends from the back sheet at an angle toward the face sheet. The at least one cell wall further coupled to the face sheet along a cell wall top edge. The resonant cell is formed in a predetermined shape and contains a volume in a space defined by the at least one cell wall, the back sheet, and the face sheet. The cell wall base edge length is greater than the cell wall top edge length.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/421,935 filed Feb. 1, 2017, currently pending, which is herebyincorporated by reference herein.

BACKGROUND

The field of the disclosure relates generally to turbofan engines and,more particularly, to acoustic liners for turbofan engine components.

Aircraft engine noise can be a significant problem in high populationareas and noise-controlled environments. The noise is generally composedof contributions from various source mechanisms in the aircraft, withfan noise typically being a dominant component of the noise at take-offand landing. Fan noise propagates through the engine intake duct, and isthen radiated to the outside environment. Acoustic liners are known tobe applied on the internal walls of the nacelle to attenuate the fannoise propagating through the engine ducts. Typical acoustic liners forengines are either a single degree of freedom (SDOF) liner, or a twodegree of freedom (2DOF) liner, sometimes referred to as a double degreeof freedom (DDOF) liner.

SDOF liners are formed of a porous facing sheet backed by a single layerof cellular separator such as honeycomb cells, which itself is backed bya solid backing plate that is substantially impervious to higherfrequency noise transmission. 2DOF liners, on the other hand, are formedof two cellular layers between the porous facing sheet and the solidbacking plate, with the two cellular layers separated by a porous septumsheet. The acoustic performance of both SDOF and 2DOF liners is stronglydependent on the depth of the cells in each honeycomb layer, where thecell depth controls the internal volume of the cell that is availablefor acoustic resonance. The additional layer of the 2DOF liner allowsnoise suppression of at least one other main frequency than the SDOFliner. However, the additional layer of the 2DOF liner significantlyincreases the weight of and cost to produce the liner, including throughadditive manufacturing.

At least some known SDOF honeycomb acoustic liners attempt to achievethe multiple frequency advantages of the 2DOF liner in an SDOFconstruction by forming individual cells within the core layer to havevariable depths from the perforate facing sheet, thereby creatingdifferent resonant cavity volumes within the same SDOF layer. However,this variable depth construction requires a thicker core layer toaccommodate the depth of longer individual cells that correspond tolarger cavity volumes. Additionally, because some of the variable depthcells have shorter lengths, there is left a significant amount of solidmaterial between the bottom of the shorter cell and the backing plate,which also increases the overall weight of the core layer.

BRIEF DESCRIPTION

In one aspect, an acoustic liner includes a face sheet, a back sheetspaced from said face sheet, and a core layer. The core layer includes aplurality of adjacent cavities extending between said face sheet andsaid back sheet. A thickness of the core layer is defined by a distancebetween said face sheet and said back sheet. The core layer furtherincludes a plurality of first resonant cells, each first resonant cellof said plurality of first resonant cells includes at least one firstcell wall coupled to the back sheet along a first cell wall base edge.The at least one cell wall extends from the back sheet at a first angletoward the face sheet. The at least one first cell wall is furthercoupled to the face sheet along a first cell wall top edge. The firstresonant cell is formed in a first predetermined shape and contains afirst volume in a space defined by the at least one first cell wall, theback sheet, and the face sheet. The first cell wall base edge length isgreater than the first cell wall top edge length.

In another aspect, an acoustic structure includes a core layer includingan inner side and an outer side spaced opposite the inner side across athickness defined therebetween. The acoustic structure further includesa plurality of first resonant cells occupying the thickness of the corelayer. Each first resonant cell of the plurality of first resonant cellsincludes at least one first cell wall extending at a first angle from afirst cell wall base edge along the outer side to a first cell wall topedge along the inner side. The first resonant cell is formed in a firstpredetermined shape. The first resonant cell contains a first volume ina space defined by the at least one cell wall, the inner side, and theouter side. A length of the first cell wall base edge is greater than alength of the first cell wall top edge.

In still another aspect, a method of attenuating noise from a sourcegenerating a sound wave stream includes receiving a sound wave streamincluding a plurality of frequency components at a first surface of acore layer of an acoustic structure, the core layer including aplurality of resonant cells occupying a thickness of the core layer andchanneling the sound wave stream into the core layer. The method furtherincludes reflecting the sound wave stream from a first surface of afirst resonant cell of the plurality of resonant cells to a secondsurface of a second resonant cell of the plurality of resonant cells, atleast partially canceling at least some of the plurality of frequencycomponents based on the reflecting, and absorbing a portion of an energycontent of the reflected sound wave stream at each reflection.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a perspective partial cutaway view of a turbofan engine.

FIG. 2 is an isometric partial cutaway view of a portion of an acousticliner that may be used with the turbofan engine depicted in FIG. 1.

FIG. 3 is a perspective view of the cellular structure of a core layerof the acoustic liner shown in FIGS. 1 and 2.

FIG. 4 is a perspective view of the cellular structure of an alternativeembodiment of the core layer shown in FIGS. 2 and 3.

FIG. 5 is a perspective view of the cellular structure of anotheralternative embodiment of the core layer shown in FIGS. 2 and 3.

FIG. 6 is a perspective view of the cellular structure of yet anotheralternative embodiment of the core layer shown in FIGS. 2 and 3 depictedin a non-annular version.

FIG. 7 is a perspective view of the cellular structure of still anotheralternative embodiment of the core layer shown in FIGS. 2 and 3 depictedin a non-annular version.

FIG. 8 is a pan view of the cellular structure of the core layer shownin FIGS. 2 and 3 depicted in a non-annular version.

FIG. 9 is a sectional view of the core layer shown in FIG. 8.

FIG. 10 is a perspective view of the cellular structure of yet anotheralternative embodiment of the core layer shown in FIGS. 2 and 3 depictedin a non-annular version.

FIG. 11 is a perspective view of the cellular structure of the corelayer shown in FIG. 4 depicted in a non-annular version.

FIG. 12 is a pan view of the cellular structure of another alternativeembodiment of the core layer shown in FIGS. 2 and 3 depicted in anon-annular version.

FIG. 13 is a perspective view of the core layer shown in FIG. 12.

FIG. 14 is an isometric partial cutaway view of a portion of yet anotheralternative embodiment of the core layer shown in FIGS. 2 and 3 depictedin a non-annular version.

FIG. 15 is a perspective view of the cellular structure of the corelayer shown in FIG. 14.

FIG. 16 is a graphical representation of operation of the core layer ofthe acoustic liner shown in FIGS. 7 and 8.

FIG. 17 is a schematic diagram of noise certification points whereeffective perceived noise level (EPNL) values are determined in ameasurement scheme for the core layer of the acoustic liner shown inFIGS. 7 and 8.

FIG. 18 is a flow chart of an exemplary method of attenuating noise froma source generating a sound wave stream that may be used with the corelayer of the acoustic liner shown in FIGS. 7 and 8.

FIG. 19 is a side elevation view of another embodiment of the acousticliner shown in FIG. 1 in accordance with an example embodiment of thepresent disclosure.

FIG. 20 is a side elevation view of the acoustic liner shown in FIG. 1in accordance with another example embodiment of the present disclosure.

Unless otherwise indicated, the drawings provided herein are meant toillustrate features of embodiments of this disclosure. These featuresare believed to be applicable in a wide variety of systems including oneor more embodiments of this disclosure. As such, the drawings are notmeant to include all conventional features known by those of ordinaryskill in the art to be required for the practice of the embodimentsdisclosed herein.

DETAILED DESCRIPTION

In the following specification and the claims, reference will be made toa number of terms, which shall be defined to have the followingmeanings.

The singular forms “a,” “an,” and “the” include plural references unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” “approximately,” and “substantially,” are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged; such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.Additionally, well-known elements, devices, components, methods, processsteps and the like may not be set forth in detail in order to avoidobscuring the invention.

A system for attenuating turbine engine noise is described herein.Features of the discussion and claims may be applied to various classesof engines including, turbojets, turbofans, turboprops, turboshafts,ramjets, rocket jets, pulse-jets, turbines, gas turbines, steamturbines, commercial engines, corporate engines, military engines,marine engines, etc. As used herein “turbine engine” includes enginesother than, and in addition to, aircraft engines.

Sizes and shapes of cells forming an acoustic line of the soundattenuating system are selected to attenuate a certain range offrequencies that interact with shapes and sizes of cells by extracting amaximum amount of sound energy from the sound wave at each interactionwith the cells.

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 1 shows a generalorientation of a turbofan engine 100 in a perspective partial cutawayview, in accordance with an exemplary embodiment of the presentdisclosure. In the exemplary embodiment, turbofan engine 100 is embodiedin a high-bypass turbofan jet engine for powering an aircraft (notshown) in flight. Turbofan engine 100 typically will be attached to thewings, fuselage, or tail (also not shown) of the aircraft throughappropriate mountings.

Turbofan engine 100 includes a nacelle 102 surrounding a fan rotor 104,which includes a plurality of circumferentially spaced fan blades 106powered by power turbine 108. Nacelle 102 defines a fan duct 110 havinga duct inner wall 112 that receives an ambient inlet airflow 114 flowingdownstream through fan rotor 104 along a longitudinal axial centerline116. An acoustic liner 118 has an annular construction and is disposedalong duct inner wall 112. In an exemplary embodiment, acoustic liner118 is formed as an arcuate cylindrical acoustic liner 118 and ispositioned along duct inner wall 112 upstream of fan blades 106 at aninner barrel 119 portion of nacelle 102. Additionally or alternatively,acoustic liner 118 is disposed along duct inner wall 112 radiallyoutboard of fan blades 106 at a fan casing portion 120 of nacelle 102.In various embodiments, acoustic liner 118 is disposed along duct innerwall 112 downstream of fan blades 106 at a transcowl portion 122 ofnacelle 102, and/or along non-rotating portions of fan casing portion120 or other components, ducts, or casings within turbofan engine 100where noise suppression (e.g., attenuation) is appropriate, such as, butnot limited to core cowl portion 124, or which are capable ofintercepting and suppressing noise having a predetermined range offrequencies.

As used herein, the terms “upstream” and “downstream” generally refer toa position in a jet engine in relation to the ambient air inlet and theengine exhaust at the back of the engine. For example, the inlet fan isupstream of the combustion chamber. Likewise, the terms “fore” and “aft”generally refer to a position in relation to the ambient air inlet andthe engine exhaust nozzle.

In operation, fan rotor 104 rotates within fan casing portion 120,producing discrete tonal noise predominately at a blade passagefrequency (BPF) and multiples thereof. During take-off of the aircraft,when fan blades 106 of fan rotor 104 reach transonic and supersonicrotational velocities during operation, noise is generated therefrom andpropagated out of the fan duct 110 into the surrounding environment. Inthe exemplary embodiment, acoustic liner 118 serves to suppress noiseresonating at the BPF and harmonics of the BPF. Acoustic liner 118 isconfigured to facilitate reducing the sound level of waves radiatingfrom fan duct 110. In some embodiments, acoustic liner 118 is configuredto absorb one or more components of the sound waves and thereby reducingthe sound at specific frequencies. In other embodiments, acoustic liner118 is able to reflect incident sound waves multiple times before thesound wave is able to escape acoustic liner 118. Multiple reflectionsserve to reduce the amplitude of the sound waves. Additionally, acousticliner 118 can cause the sound waves to become out-of-phase, which tendsto cancel at least some of the energy in the sound waves.

FIG. 2 is an isometric partial cutaway view of a portion of acousticliner 118 depicted in FIG. 1, disposed proximate airflow 114, inaccordance with an exemplary embodiment. Acoustic liner 118 includes acore layer 200 topped by a face sheet 202. In the exemplary embodiment,face sheet 202 includes a plurality of perforations 203 extendingthrough a material of construction of face sheet 202, and positioned andspaced therein in at least one of a regular repeating pattern and arandom pattern. Core layer 200 is backed by a substantially imperforateback sheet 204 spaced from and opposing face sheet 202, and positionedgenerally axisymmetric face sheet 202. Referring to FIG. 1, back sheet204, face sheet 202, and core layer 200 of acoustic liner 118 is formedas an arcuate cylindrical acoustic liner 118, as portion of which isdepicted in FIG. 2. A noise source (e.g., fan blades 106 of fan rotor104) is thus positioned within arcuate cylindrical acoustic liner 118with face sheet 202 facing the noise source, and back sheet 204 moredistal from noise source relative to face sheet 202. In an alternativeembodiment, not shown, back sheet 204, face sheet 202, and core layer200 of acoustic liner 118 is formed as a substantially flat acousticliner 118. For example, and without limitation, a noise source ispositioned in an enclosed volume such as a room containing noisymachinery, where the planar walls of the room are at least partiallyformed with substantially flat acoustic liner 118. In still otherembodiments, not shown, back sheet 204, face sheet 202, and core layer200 of acoustic liner 118 is formed as a complexly curved acoustic liner118. For example, and without limitation, one or more complexly curvedwalls of a noise source-containing room are at least partially formedwith complexly curved acoustic liner 118.

Core layer 200 includes a cellular structure formed of a plurality ofadjacent cavities 206 that extend between face sheet 202 and back sheet204. A thickness 207 of cavities 206 and core layer 200 is defined by adistance taken along a radial axis R (also shown in FIG. 1) between facesheet 202 and back sheet 204. In the exemplary embodiment, each cavity206 of plurality of cavities 206 is defined by openings 208 between aplurality of first resonant cells 209 positioned adjacent one another.Each first resonant cell 209 of plurality of first resonant cells 209includes at least one first cell wall 210 which defines a partitionbetween adjacent cavities 206.

Face sheet 202 is attached to an inner side 212 of core layer 200 andback sheet 204 is attached to an outer side 214 of core layer 200. Outerside 214 defines a first curved surface and inner side 212 defines asecond curved surface. In this exemplary embodiment, the terms “inner”and “outer” refer to the orientation of the respective layers inrelation to longitudinal axial centerline 116, shown in FIG. 1. In theexemplary embodiment, acoustic liner 118 is formed unitarily using anadditive manufacturing process. In one embodiment, back sheet 204 isformed in an additive manufacturing process, and plurality of firstresonant cells 209 are formed thereupon by additive manufacturing. Insome embodiments, additional cell walls are formed by an additivemanufacturing process between adjacent first resonant cells 209 as shownand described in detail below.

Further, in the exemplary embodiment, face sheet 202, includingperforations 203 thereof, is formed upon completing forming firstresonant cells 209 by additive manufacturing. As used herein, “additivemanufacturing” refers to any process which results in athree-dimensional (3D) object and includes a step of sequentiallyforming the shape of the object one layer at a time. Additivemanufacturing processes include, for example, 3D printing,laser-net-shape manufacturing, direct laser sintering, direct lasermelting, selective laser sintering (SLS), plasma transferred arc,freeform fabrication, stereolithography (SLA), and the like. Additivemanufacturing processes can employ liquid materials, solid materials,powder materials, or wire as a raw material. Moreover, additivemanufacturing processes can generally relate to a rapid way tomanufacture an object (article, component, part, product, etc.) where aplurality of thin unit layers are sequentially formed to produce theobject. For example, layers of a liquid material may be provided (e.g.,laid down) and irradiated with an energy beam (e.g., laser beam) so thateach layer are sequentially cured to solidify the layer.

In various embodiments, core layer 200 is formed using other processes,such as, but not limited to, casting or injection molding orelectroforming, or coldspray.

In an alternative embodiment, face sheet 202 and back sheet 204 can beattached to core layer 200 by adhesive bonding, for example, by thermal,sonic, and or electric welding processes. Acoustic liner 118 is securedwithin turbofan engine 100 by attachment with duct inner wall 112 (shownin FIG. 1). In various embodiments, acoustic liner 118 is attached toengine 100 (shown in FIG. 1) via a flange joining it to the fan casingportion 120. Further, in an alternative embodiment, face sheet 202 isformed of a porous material, such as a wire mesh, a perforated sheet, ora woven or nonwoven fibrous material. In some embodiments, core layer200 is molded, or fabricated by an additive or accumulativemanufacturing process, such as 3-D printing, as described above. Theability of acoustic liner 118 to attenuate noise at a desired frequency,or range of frequencies, is dependent on its acoustic impedance, whichis a function of a number of parameters, including thickness 207 of corelayer 200 and shapes of cavities 206 and first resonant cells 209, aswell as resident volumes contained therein, and an angle at which afirst cell wall base edge 216 of first cell wall 210 extends from backsheet 204 to face sheet 202. Face sheet 202, back sheet 204, and corelayer 200 of acoustic liner 118 may be formed of various materials thatalso may have an effect on the acoustic impedance of acoustic liner 118.For example, face sheet 202, back sheet 204, and/or core layer 200 maybe formed of thermoplastic materials, such as, but not limited to,polyamide-imides (PAD, acrylonitrile butadiene styrene (ABS),polyetherimide (PEI), polyether ether ketone (PEEK). Additionally, facesheet 202, back sheet 204, and/or core layer 200 may be formed ofthermoset materials, such as, but not limited to, epoxy, acrylic,vinylester, polyurethane, silicone, polyimide, cyanate ester, polyester.Further face sheet 202, back sheet 204, and/or core layer 200 may beformed of metals such as, but not limited to, aluminum, nickel,titanium, steel, cobalt chrome, nickel cobalt, and or a nickel-ironalloy having a low coefficient of thermal expansion (CTE).

FIG. 3 is a perspective view of the cellular structure of core layer 200of acoustic liner 118, as shown in FIGS. 1 and 2. For illustrativepurposes face sheet 202 is removed from the view illustrated in FIG. 3.As illustrated in FIG. 3, plurality of first resonant cells 209 arepositioned on back sheet 204 in a grid arrangement, where outer side 214of core layer 200 forms a rectangular grid by a tessellation of regularrectangular openings 208 (shown in FIG. 2) that generally align in acurved surface where outer side 214 fixedly joins back sheet 204. Eachfirst resonant cell 209 of plurality of first resonant cells 209 coupledto back sheet 204 has an equivalent first shape. In the exemplaryembodiment, first resonant cell 209 is embodied in a first shapedefining a regular, right, truncated pyramid 302 with four faces 304having approximately equal areas. Truncated pyramid 302 includes a firstpolygonal base 306 embodied in a square with four sides (e.g., n=4),each of which defines first cell wall base edge 216 with first length308 along which a respective first cell wall 210 of first resonant cell209 is coupled to back sheet 204. In the exemplary embodiment, a sum offirst lengths 308 of respective first cell walls 210 defines a firstperimeter along which first resonant cell 209 is coupled to back sheet204.

Also, in the exemplary embodiment, truncated pyramid 302 includes asubstantially planar frustum 310 that is substantially axisymmetric tofirst polygonal base 306. Frustum 310 is embodied in a square with foursides, each of which defines a first cell wall top edge 311 with asecond length 312 along which respective first cell wall 210 of firstresonant cell 209 is coupled to face sheet 202 (not shown). In theexemplary embodiment, a sum of second lengths 312 of respective firstcell walls 210 defines a second perimeter along which first resonantcell 209 is coupled to face sheet 202. Furthermore, first shape oftruncated pyramid 302-type first resonant cell 209 contains a firstvolume in a space therein defined by first cell walls 210 thereof, backsheet 204, and face sheet 202.

FIG. 4 is a perspective view of the cellular structure of an alternativeembodiment of core layer 200 of acoustic liner 118. For illustrativepurposes face sheet 202 is removed from the view illustrated in FIG. 4.As illustrated in FIG. 4, plurality of first resonant cells 209 arepositioned on back sheet 204 in a grid arrangement, where outer side 214of core layer 200 forms a rectangular grid by a tessellation of regularrectangular openings 208 (shown in FIG. 2) that generally align in acurved surface where outer side 214 fixedly joins back sheet 204. In thealternative embodiment, respective shapes of first resonant cells 209alternate in an axial direction (A). Each first row 402 of a pluralityof first rows 402 includes a plurality of first resonant cells 209embodied in first shape defining regular, right, truncated pyramid 302,as shown and described above with reference to FIG. 3. Each second row404 of a plurality of second rows 404 includes a plurality of firstresonant cells 209 embodied in first shape defining a regular, right,non-truncated pyramid 406. First row 402 and second row 404 thusalternate in the axial direction (A). Non-truncated pyramid 406 hasfirst polygonal base 306 with four sides, each of which defines firstlength 308, a sum of which defines first perimeter along whichrespective first cell walls 408 of non-truncated pyramid 406-type firstresonant cell 209 are coupled to back sheet 204. In the alternativeembodiment, first perimeters of non-truncated pyramid 406-type firstresonant cells 209 are approximately equal to first perimeters oftruncated pyramid 302-type first resonant cells. In other embodiments,not shown, non-truncated pyramid 406-type first resonant cells 209 havefirst perimeters that are different from first perimeters of truncatedpyramid 302-type first resonant cells.

Also, in the alternative embodiment, non-truncated pyramid 406 does notinclude substantially planar frustum 310, but rather includes an apex410 defining second length 312 (shown in FIG. 3) that is approximatelyequal to 0 (zero). Apex 410 thus defines a point at which respectivefirst cell walls 408 are coupled to face sheet 202. Further, in thealternative embodiment, apex 410 defines inner side 212 of core layer200, and a distance from back sheet 204 to apex 410 defines thickness207. Similarly, frustum 310 also defines inner side 212, and a distancefrom back sheet 204 to frustum 310 also defines thickness 207. The firstvolume is defined by back sheet 204, face sheet 202, and first cellwalls 408 of non-truncated pyramid 406-shaped first resonant cell 209.

FIG. 5 is a perspective view of the cellular structure of anotheralternative embodiment of core layer 200 of acoustic liner 118. Forillustrative purposes face sheet 202 is removed from the viewillustrated in FIG. 5. As illustrated in FIG. 5, plurality of firstresonant cells 209 are positioned on back sheet 204 in a gridarrangement, where outer side 214 of core layer 200 forms a rectangulargrid by a tessellation of regular rectangular openings 208 (shown inFIG. 2) that generally align in a curved surface where outer side 214fixedly joins back sheet 204. In this alternative embodiment, respectiveshapes of first resonant cells 209 alternate in a circumferentialdirection (C). Each first column 502 of a plurality of first columns 502includes a plurality of first resonant cells 209 embodied in first shapedefining regular, right, truncated pyramid 302, as shown and describedabove with reference to FIG. 3. Each second column 504 of a plurality ofsecond columns 504 includes a plurality of first resonant cells 209embodied in first shape defining a regular, oblique non-truncatedpyramid 506. First column 502 and second column 504 thus alternate inthe circumferential direction (C). Oblique non-truncated pyramid 506 hasfirst polygonal base 306 with four sides, each of which defines firstlength 308, a sum of which defines first perimeter along whichrespective first cell walls 508 of oblique non-truncated pyramid506-type first resonant cell 209 are coupled to back sheet 204. In thisalternative embodiment, first perimeters of oblique non-truncatedpyramid 506-type first resonant cells 209 are approximately equal tofirst perimeters of truncated pyramid 302-type first resonant cells. Inother embodiments, not shown, oblique non-truncated pyramid 506-typefirst resonant cells 209 have first perimeters that are different fromfirst perimeters of truncated pyramid 302-type first resonant cells.

Also, in this alternative embodiment, oblique non-truncated pyramid 506does not include substantially planar frustum 310, but rather includesan apex 510 defining second length 312 (shown in FIG. 3) that isapproximately equal to 0 (zero). Apex 510 thus defines a point at whichrespective first cell walls 508 are coupled to face sheet 202, thusfurther defining inner side 212 of core layer 200, where a distance fromback sheet 204 to apex 510 defines thickness 207. Likewise, frustum 310also defines inner side 212, and a distance from back sheet 204 tofrustum 310 also defines thickness 207. The first volume is defined byback sheet 204, face sheet 202, and first cell walls 508 of obliquenon-truncated pyramid 506-shaped first resonant cell 209.

FIG. 6 is a perspective view of the cellular structure of yet anotheralternative embodiment of core layer 200 of acoustic liner 118, butdepicted in a non-annular version. For illustrative purposes face sheet202 is removed from the view illustrated in FIG. 6. As illustrated inFIG. 6, plurality of first resonant cells 209 are positioned on backsheet 204 in a grid arrangement, where outer side 214 of core layer 200forms a rectangular grid by a tessellation of regular rectangularopenings 208 (shown in FIG. 2) that generally align in a plane whereouter side 214 fixedly joins back sheet 204. Each first resonant cell209 of plurality of first resonant cells 209 coupled to back sheet 204has an equivalent first shape embodied in non-truncated pyramid 406.First cell walls 408 extend from back sheet 204 to face sheet 202 at afirst angle 602. First cell walls 408 of non-truncated pyramid 406couple to face sheet 202 at a first point 604 defined by apex 410 andhaving second length 312 (shown in FIG. 3) approximately equal to 0, asshown and described above with reference to FIG. 4. A space defined byfirst cell walls 408 of respective non-truncated pyramid 406-type firstresonant cells 209, back sheet 204, and face sheet 202 contains a firstvolume 606 therein.

In this alternative embodiment, core layer 200 of acoustic liner 118includes a plurality of second resonant cells 608 having four secondcell walls 610. Second cell wall 610 is formed as a triangular planarsheet spanning first points 604 of two adjacent non-truncated pyramid406-type first resonant cells 209 and a second point 612 defined wherefour adjacent non-truncated pyramid 406-type first resonant cells 209meet on back sheet 204. Second cell wall 610 is coupled to face sheet202 along a second cell wall base edge 613 with a third length 614. Asum of third lengths 614 of respective second cell walls 610 defines athird perimeter along which second resonant cell 608 is coupled to facesheet 202.

Second cell wall 610 also extends from each of the two respective firstpoints 604 on face sheet 202 at a second angle 616 to second point 612on back sheet 204. In this alternative embodiment, second angle 616 isapproximately equal to first angle 602. Also, in this alternativeembodiment, second cell wall 610 is coupled to back sheet 204 at secondpoint 612, where second point 612 defines a fourth length less thanthird length 614 and approximately equal to 0. Thus, in this alternativeembodiment, second resonant cell 608 defines a polyhedral second shapehaving approximately equivalent dimensions as non-truncated pyramid406-type first resonant cells 209 (e.g., second point 612 defining anapex of second shape and third length 614 approximately equal to firstlength 308, as shown and described above with reference to FIG. 4), butwhere second shape has an opposite orientation relative to first shapewith respect to face sheet 202 and back sheet 204. Here, second shapedefines a regular, right, non-truncated pyramid polyhedron having fourequilateral triangle faces embodied in four second cell walls 610, andthird perimeter defines a square polygonal base having four sides, whereeach side has third length 614. Therefore, in this alternativeembodiment, four second cell walls 610 of second resonant cell 608 arecoupled to face sheet 202 along third perimeter. Further, in thisalternative embodiment, a space defined by second cell walls 610 ofrespective second resonant cells 608, back sheet 204, and face sheet 202contains a second volume 618 therein, where second volume 618 isapproximately equal to first volume 606.

Also, in this alternative embodiment, core layer 200 of acoustic liner118 includes a plurality of third resonant cells 620. Third resonantcell 620 defines a third shape (e.g., a regular non-pyramidal polyhedronwith four equilateral triangle faces) that is different from first shapeand second shape. Third shape is further defined by two first points 604and two second points 612 of two adjacent non-truncated pyramid 406-typefirst resonant cells 209. Further, in this alternative embodiment, thirdresonant cell 620 has a third volume 622 defined by two opposing firstcell walls 408, two adjacent second cell walls 610, back sheet 204, andface sheet 202. Thus, in this alternative embodiment, a total volume ofcore layer 200 in acoustic liner 118 is approximately equal to a sum offirst volumes 606, second volumes 618, and third volumes 622, ofplurality of first resonant cells 209, plurality of second resonantcells 608, and plurality of third resonant cells 620, respectively.

FIG. 7 is a perspective view of the cellular structure of still anotheralternative embodiment of core layer 200 of acoustic liner 118, butdepicted in a non-annular version. For illustrative purposes face sheet202 is removed from the view illustrated in FIG. 7. As illustrated inFIG. 7, plurality of first resonant cells 209 are positioned on backsheet 204 in a spaced arrangement, where, in the axial (A) direction,adjacent first resonant cells 209 are separated by a first gap distance702 and where, in the circumferential (C) direction, adjacent firstresonant cells 209 are separated by a second gap distance 704. In thisalternative embodiment, first gap distance 702 is approximately equal tosecond gap distance 704. In other embodiments, not shown, second gapdistance 704 is different from first gap distance 702.

In this alternative embodiment, each first resonant cell 209 ofplurality of first resonant cells 209 coupled to back sheet 204 has anequivalent first shape embodied in truncated pyramid 302. First cellwalls 210 extend from back sheet 204 to face sheet 202 at first angle602. Four first cell walls 210 of truncated pyramid 302 are coupled toface sheet 202 along second perimeter of frustum 310. In thisalternative embodiment, frustum 310 has four sides, each having secondlength 312 greater than 0, and where frustum 310 is further defined byfour frustum points 705. Frustum points 705 include, in clockwise orderas illustrated in FIG. 7, a first frustum point 706, a second frustumpoint 708, a third frustum point 710, and a fourth frustum point 712. Aspace defined by first cell walls 210 of respective truncated pyramid302-type first resonant cells 209, back sheet 204, and face sheet 202(e.g., at frustum 310) contains a first volume 714 therein.

In this alternative embodiment, core layer 200 of acoustic liner 118includes a plurality of second resonant cells 716 having four secondcell walls 718. Second cell wall 718 is formed as a trapezoidal planarsheet spanning two frustum points 705 of adjacent frustums 310 and twocorner points 720 of adjacent corners 722 of first polygonal bases 306of adjacent truncated pyramid 302-type first resonant cells 209. Secondcell wall 718 is coupled to face sheet 202 along a second cell wall baseedge 723 with a third length 724. A sum of third lengths 724 ofrespective second cell walls 718 defines a third perimeter along whichsecond resonant cell 716 is coupled to face sheet 202.

Second cell wall 718 also extends from each of the two respectivefrustum points 705 on face sheet 202 at a second angle 616 to respectivecorner points 720 on back sheet 204. In this alternative embodiment,second angle 616 is approximately equal to first angle 602. In otherembodiments, not shown, second angle 616 is different from first angle602 where, for example, and without limitation, first resonant cell 209is embodied in at least one of an irregular truncated pyramid and anoblique truncated pyramid. Also, in this alternative embodiment, secondcell wall 718 is coupled to back sheet 204 along a second cell wall topedge 732 with a fourth length 725 less than third length 724 and greaterthan 0. Thus, in this alternative embodiment, second resonant cell 716defines a polyhedral second shape having approximately equivalentdimensions as truncated pyramid 302-type first resonant cell 209 (e.g.,four corner points 720 defining a square-shaped frustum and third length724 approximately equal to first length 308, as shown and describedabove with reference to FIG. 3), but where second shape has an oppositeorientation relative to first shape with respect to face sheet 202 andback sheet 204. Here, second shape defines a regular, right, truncatedpyramid polyhedron having four trapezoidal faces embodied in four secondcell walls 718, and third perimeter defines a square polygonal basehaving four sides, where each side has third length 724. Therefore, inthis alternative embodiment, four second cell walls 718 of secondresonant cell 716 are coupled to face sheet 202 along third perimeter.Further, in this alternative embodiment, a space defined by second cellwalls 718 of respective second resonant cells 716, back sheet 204, andface sheet 202 contains a second volume 726 therein, where second volume726 is approximately equal to first volume 714.

Also, in this alternative embodiment, core layer 200 of acoustic liner118 includes a plurality of third resonant cells 728. Third resonantcell 728 defines a third shape (e.g., an irregular non-pyramidalpolyhedron with four trapezoidal faces and two rectangular faces) thatis different from first shape and second shape. Third shape is furtherdefined by four frustum points 705 and four corner points 720 of twoadjacent truncated pyramid 302-type first resonant cells 209. Further,in this alternative embodiment, third resonant cell 728 has a thirdvolume 730 defined by two opposing first cell walls 210, two adjacentsecond cell walls 718, back sheet 204, and face sheet 202. Thus, in thisalternative embodiment, a total volume of core layer 200 in acousticliner 118 is approximately equal to a sum of first volumes 714, secondvolumes 726, and third volumes 730, of plurality of first resonant cells209, plurality of second resonant cells 716, and plurality of thirdresonant cells 728, respectively.

In other embodiments, not shown, and where, for example, and withoutlimitation, first gap distance 702 is different from second gap distance704, each of first shape, second shape, and third shape have a differentshape relative to one another. In such other embodiments, plurality offirst resonant cells 209 all have the same shape with the samedimensions. However, where first gap distance 702 is less than secondgap distance 704, second shape is embodied in an irregular, right,truncated pyramid and necessarily has a different shape than firstshape. Similarly, as opposed to embodiments such as those shown anddescribed above with reference to FIGS. 6 and 7, core layer 200 ofacoustic liner 118 need not have regular spacing of plurality of firstresonant cells 209 on back sheet 204, and by extension, need not haveregular arrangements of spacing of plurality of first resonant cells209, second resonant cells 716, and third resonant cells 728. Forexample, and without limitation, first gap distance 702 varied randomlyin the axial (A) direction between a zero-valued distance (e.g., as inthe embodiment shown in FIG. 6) to a non-zero-valued distance (e.g., asin the embodiment shown in FIG. 7) results in a random distribution ofsecond volumes 726 and third volumes 730 in the axial (A) direction.Similarly, second gap distance 704 varied randomly in thecircumferential (C) direction between zero-valued and non-zero-valueddistances results in a random distribution of second volumes 726 andthird volumes 730 in the circumferential (C) direction. Further, instill other embodiments, not shown, shapes and/or dimensions of firstresonant cells 209 are varied randomly in at least one of the axial (A)direction and the circumferential (C) direction, resulting in randomdistributions of first volumes 714 in the respective directions, inaddition to random distributions of second volumes 726 and third volumes730.

FIG. 8 is a pan view of the cellular structure of the exemplaryembodiment of acoustic liner 118 core layer 200 shown in FIG. 2, butdepicted in a non-annular version. FIG. 9 is a sectional view of theacoustic liner 118 core layer 200 shown in FIG. 8 taken along a sectionline labeled “S-S”. For illustrative purposes face sheet 202 is removedfrom the view illustrated in FIG. 8. Referring to FIG. 8, plurality offirst resonant cells 209 are positioned on back sheet 204 in a gridarrangement, where, in contrast to the embodiment shown and describedabove with reference to FIG. 7, first gap distance 702 and second gapdistance 704 are each approximately equal to 0.

In this alternative embodiment, each first resonant cell 209 ofplurality of first resonant cells 209 coupled to back sheet 204 has anequivalent first shape embodied in truncated pyramid 302. Four firstcell walls 210 of truncated pyramid 302 are coupled to face sheet 202along second perimeter of frustum 310 with sides having second length312 defined between frustum points 705, as shown and described abovewith reference to FIG. 3. A space defined by first cell walls 210 ofrespective truncated pyramid 302-type first resonant cells 209, backsheet 204, and face sheet 202 (e.g., at frustum 310) contains a firstvolume 814 therein.

In this alternative embodiment, core layer 200 of acoustic liner 118includes a plurality of second resonant cells 816 having four secondcell walls 818. Second cell wall 818 is formed as a triangular planarsheet spanning two frustum points 705 of adjacent frustums 310 and ashared corner point 820 of shared corners 822 of first polygonal bases306 of adjacent truncated pyramid 302-type first resonant cells 209.Second cell wall 818 is coupled to face sheet 202 along a second cellwall base edge 823 with a third length 824. A sum of third lengths 824of respective second cell walls 818 defines a third perimeter alongwhich second resonant cell 816 is coupled to face sheet 202.

Also, in this alternative embodiment, second cell wall 818 is coupled toback sheet 204 at a respective corner point 820 having a fourth lengthapproximately equal to 0. Thus, second resonant cell 816 defines aregular, right, non-truncated pyramid second shape having an apexdefined by shared corner point 820 having approximately equivalentdimensions as truncated pyramid 302-type first resonant cell 209, butwhere second shape has an opposite orientation relative to first shapewith respect to face sheet 202 and back sheet 204. Therefore, in thisalternative embodiment, four second cell walls 818 of second resonantcell 816 are coupled to face sheet 202 along third perimeter. Further,in this alternative embodiment, a space defined by second cell walls 818of respective second resonant cells 816, back sheet 204, and face sheet202 contains a second volume 826 therein.

Also, in this alternative embodiment, core layer 200 of acoustic liner118 includes a plurality of third resonant cells 828. Third resonantcell 828 defines a third shape (e.g., an irregular non-pyramidalpolyhedron with two trapezoidal faces, two triangular faces, and onerectangular face) that is different from first shape and second shape.Third shape is further defined by four frustum points 705 and two cornerpoints 820 of two adjacent truncated pyramid 302-type first resonantcells 209. Further, third resonant cell 828 has a third volume 830defined by two opposing first cell walls 210, two adjacent second cellwalls 818, back sheet 204, and face sheet 202. Thus, in this alternativeembodiment, a total volume of core layer 200 in acoustic liner 118 isapproximately equal to a sum of first volumes 814, second volumes 826,and third volumes 830, of plurality of first resonant cells 209,plurality of second resonant cells 816, and plurality of third resonantcells 828, respectively.

Referring now to FIG. 9, first cell walls 210 extend from back sheet 204to face sheet 202 at first angle 602. Second cell wall 818 also extendsfrom each of first frustum point 706 and second frustum point 708 onface sheet 202 at second angle 616 to respective shared corner points820 on back sheet 204. In this alternative embodiment, second angle 616is approximately equal to first angle 602. In other embodiments, notshown, second angle 616 is different from first angle 602 where, forexample, and without limitation, first resonant cell 209 is embodied inat least one of an irregular truncated pyramid and an oblique truncatedpyramid.

Also, in this alternative embodiment, thickness 207 is approximatelyequal to 1 (one) inch, first length 308 is approximately equal to ¾(three-fourths) of 1 inch, and second length 312 is approximately equalto ⅜ (three-eights) of 1 inch. Further, in the alternative embodiment, aspacing distance 902 between perforation centerlines 904 of eachperforation 203 of plurality of perforations 203 is approximately equalto second length 312, and a perforation diameter 906 is approximatelyequal to 1/20 (one twentieth) of 1 inch. In other embodiments, notshown, at least one of first length 308, second length 312, spacingdistance 902, and perforation diameter 906 have values different fromthose values specified above. Furthermore, perforations 203 arepositioned on face sheet 202 proximate frustum 310, second resonant cell816, and third resonant cell 828 to facilitate fluid and gas exchangebetween first volume 814 and an exterior 908 of acoustic liner 118 toenable drying of core layer 200 following its deployment under wetand/or humid operating conditions.

FIG. 10 is a perspective view of the cellular structure of yet anotheralternative embodiment of core layer 200 of acoustic liner 118 shown inFIG. 2, but depicted in a non-annular version. For illustrative purposesface sheet 202 is removed from the view illustrated in FIG. 10. Asillustrated in FIG. 10, plurality of first resonant cells 209 arepositioned on back sheet 204 in an offset arrangement, where cornerpoints 720 are not shared amongst plurality of adjacent first resonantcells 209. In this alternative embodiment, first gap distance 702 andsecond gap distance 704 (as shown and described above with reference toFIG. 7) are each approximately equal to 0. In other embodiments, notshown, at least one of first gap distance 702 and second gap distance704 is greater than 0, which results in an increase in a number ofcorner points 720.

In this alternative embodiment, core layer 200 of acoustic liner 118includes a plurality of second resonant cells 802 having two second cellwalls 804. Second cell wall 804 is formed as a triangular planar sheetspanning two frustum points 705 of adjacent frustums 310 and one sharedcorner point 720 of first polygonal bases 306 of adjacent truncatedpyramid 302-type first resonant cells 209. Second cell wall 804 iscoupled to face sheet 202 along a second cell wall base edge 805 with athird length 806. A sum of third lengths 806 of respective second cellwalls 804 plus a sum of two second lengths 312 of opposing first cellwalls 210 (e.g., between first frustum point 706 and fourth frustumpoint 712, and between second frustum point 708 and third frustum point710) defines a third perimeter along which second resonant cell 802 iscoupled to face sheet 202.

Second cell wall 804 also extends from respective frustum points 705 onface sheet 202 at a second angle 616 to respective corner points 720 onback sheet 204. In this alternative embodiment, second angle 616 isapproximately equal to first angle 602. In other embodiments, not shown,second angle 616 is different from first angle 602 where, for example,and without limitation, first resonant cell 209 is embodied in at leastone of an irregular truncated pyramid and an oblique truncated pyramid.Also, in this alternative embodiment, second cell wall 804 is coupled toback sheet 204 along at a respective corner point 720 (e.g., having afourth length approximately equal to 0). Thus, in this alternativeembodiment, second resonant cell 802 defines an irregular polyhedralsecond shape having a different shape than first shape. Further, in thisalternative embodiment, a space defined by second cell walls 804 ofrespective second resonant cells 802, back sheet 204, and face sheet 202contains a second volume 808 therein. In other embodiments, not shown,core layer 200 illustrated in FIG. 10 further includes a plurality ofthird resonant cells. In such other embodiments, third resonant cellsinclude third cell walls formed as substantially planar sheets spanninga predetermined combination of corner points 720 and frustum points 705.Further, plurality of third cell walls are capable of being formedbetween a plurality of combinations of corner points 720 and frustumpoints 705, and therefore, plurality of third resonant cells are capableof being formed in a plurality of different third shapes.

FIG. 11 is a perspective view of the cellular structure of core layer200 of acoustic liner 118 shown in FIG. 4, but depicted in a non-annularversion. For illustrative purposes face sheet 202 is removed from theview illustrated in FIG. 11. As illustrated in FIGS. 4 and 11, pluralityof first resonant cells 209 are positioned on back sheet 204 in a gridarrangement, where outer side 214 of core layer 200 forms a rectangulargrid by a tessellation of regular rectangular openings 208 (shown inFIG. 2) that generally align in a plane where outer side 214 fixedlyjoins back sheet 204. Each first resonant cell 209 of plurality of firstresonant cells 209 coupled to back sheet 204 does not have an equivalentfirst shape. Rather, as shown in FIGS. 4 and 11, respective first shapesof first resonant cells 209 alternative in an axial direction (A), withfirst rows 402 including first resonant cells 209 a embodied in firstshape defining regular, right, truncated pyramids 302 having frustums310, and second rows 404 including first resonant cells 209 b embodiedin first shape defining regular, right, non-truncated pyramids 406having apexes 410. First cell walls 210 of first resonant cells 209 aextend from back sheet 204 to face sheet 202 at a first angle 1102, andfirst cell walls 408 of first resonant cells 209 b extend from backsheet 204 to face sheet 202 at a first angle 1104. In this alternativeembodiment, first angle 1102 is greater than first angle 1104 becausefrustum 310 and apex 410 both define thickness 207 from back sheet 204to face sheet 202.

In this alternative embodiment, the second shape also alternates in theaxial direction (A). Owing to the differing first shapes of firstresonant cell 209 a and first resonant cell 209 b, a second resonantcell 1108 a residing between first rows 402 and second rows 404 has asecond shape embodied in an irregular, right pyramid. Second resonantcell 1108 a includes four second cell walls 1110. Two second cell walls1110 a which oppose each other in the circumferential direction (C) areformed as planar triangular sheets spanning apex 410, one frustum point705, and one shared corner point 720. Second cell wall 1110 a is coupledto face sheet 202 along a second cell wall base edge 1111 a with a thirdlength 1112 a. Second cell walls 1110 a have approximately equal areas.Second cell wall 1110 b and second cell wall 1110 c oppose each other inthe axial direction (A) and have differing areas. Second cell wall 1110b is formed as a planar triangular sheet spanning two frustum points 705of adjacent frustums 310 and shared corner point 720. Second cell wall1110 c is formed as a planar triangular sheet spanning two adjacentapexes 410 and shared corner point 720. Second cell wall 1110 b iscoupled to face sheet 202 along a second cell wall base edge 1111 b witha third length 1112 b, and second cell wall 1110 c is coupled to facesheet 202 along a second cell wall base edge 1111 c with a third length1112 c greater than third length 1112 b.

Also, in this alternative embodiment, a space defined by second cellwalls 1110 of respective second resonant cells 1108 a, back sheet 204,and face sheet 202 contains a second volume 1118 therein. Also owing tothe differing first shapes of first resonant cell 209 a and firstresonant cell 209 b, a second resonant cell 1108 b residing betweensecond rows 404 and first rows 402 also has second shape embodied in anirregular, right pyramid, but with an orientation opposite to secondshape of second resonant cell 1108 a with respect to the axial direction(A). Second resonant cell 1108 b also defines a space containing secondvolume 1118 therein, as described above with reference to secondresonant cell 1108 a.

Further, in this alternative embodiment, the third shape also alternatesin the axial direction (A). Owing to the differing first shapes of firstresonant cell 209 a and first resonant cell 209 b, a third resonant cell1128 residing between adjacent first resonant cells 209 a has a thirdshape embodied in an irregular non-pyramidal polyhedron with twotrapezoidal faces, two triangular faces, and one rectangular face.Further, in this alternative embodiment, third resonant cell 1128 has athird volume 1130 defined by two opposing first cell walls 210 ofadjacent first resonant cells 209 a, two adjacent second cell walls 1110b, back sheet 204, and face sheet 202. Also owing to the differing firstshapes of first resonant cell 209 a and first resonant cell 209 b, athird resonant cell 1120 residing between adjacent first resonant cells209 b has a third shape embodied in a regular non-pyramidal polyhedronwith four equilateral triangle faces. Third resonant cell 1120 has athird volume 1122 defined by two opposing first cell walls 408 ofadjacent first resonant cells 209 b, two adjacent second cell walls 1110c, back sheet 204, and face sheet 202.

Further owing to the differing first shapes first resonant cell 209 aand first resonant cell 209 b, in this alternative embodiment, corelayer 200 includes a plurality of fourth resonant cells 1150. A fourthresonant cell 1150 a has a fourth shape embodied in an irregularnon-pyramidal polyhedron having two triangular faces with approximatelyequal areas (two adjacent second cell walls 1110 a), one additionaltriangular face defined by face sheet 202, one trapezoidal face (onefirst cell wall 210), and a fourth triangular face (one first cell wall408). Fourth resonant cell 1150 also has a fourth volume 1152 containedby a space enclosed by back sheet 204, face sheet 202, one first cellwall 210, one first cell wall 408, and two adjacent second cell walls1110 a of second resonant cells 1108 a adjoined in the circumferentialdirection (C). Also owing to the differing first shapes of firstresonant cell 209 a and first resonant cell 209 b, a fourth resonantcell 1150 b has fourth volume 1152. Fourth resonant cell 1150 b also hasfourth shape embodied in an irregular non-pyramidal polyhedron asdescribed above for fourth resonant cell 1150 a, but with an orientationopposite to fourth shape of fourth resonant cell 1150 a with respect tothe axial direction (A). Thus, in this alternative embodiment, fourthshapes of plurality of fourth resonant cells 1150 alternate in the axialdirection (A).

In other embodiments, not shown, and where, for example, and withoutlimitation, the orientations of axial direction (A) and circumferentialdirection (C) are reversed relative to the orientations illustrated inFIG. 11, at least one of second shape, third shape, and fourth shapealternate in the circumferential (C) direction. In such otherembodiments, alternation of first shape in the circumferential direction(e.g., as shown and described above with reference to FIG. 5) enablesalternation of at least one of first, second, third, and fourth shapesin the circumferential direction (C).

FIG. 12 is a plan view of the cellular structure of another alternativeembodiment of core layer 200 of acoustic liner 118 shown in FIG. 2, butdepicted in a non-annular version. FIG. 13 is a perspective view of theacoustic liner 118 core layer 200 shown in FIG. 12. For illustrativepurposes face sheet 202 is removed from the views illustrated in FIGS.12 and 13. Referring to FIG. 12, a plurality of first resonant cells1201 are positioned on back sheet 204 such that outer side 214 of corelayer 200 forms a triangular grid by a tessellation of regulartriangular openings 1202 that generally align in a plane where outerside 214 fixedly joins back sheet 204. Each first resonant cell 1201 ofplurality of first resonant cells 1201 coupled to back sheet 204 has afirst shape embodied in a non-truncated pyramid 1204, with a triangularfirst polygonal base 1205 having three sides (e.g., n=3), each havingfirst lengths 308 that sum to first perimeter. In other embodiments, notshown, at least one first resonant cell 1201 of plurality of firstresonant cells 1201 has a first shape embodied in a truncated pyramidhaving a triangular frustum with three sides each having second length312 (shown in FIG. 3) and that sum to second perimeter. First resonantcell 1201 includes three first cell walls 1206, each of which extendsfrom back sheet 204 to face sheet 202 at a first angle 1302. First cellwalls 1206 of non-truncated pyramid 1204 couple to face sheet 202 at afirst point 1208 defined by an apex 1210 and having second length 312approximately equal to 0. A space defined by first cell walls 1206 ofrespective non-truncated pyramid 1204-type first resonant cells 1201,back sheet 204, and face sheet 202 contains a first volume 1304 therein.

Referring now to FIG. 13, in this alternative embodiment, core layer 200includes a plurality of second resonant cells 1306 having two secondcell walls 1307. Second cell wall 1307 is formed as a triangular planarsheet spanning two apexes 1210 of adjacent first resonant cells 1201 andone shared corner point 720. Second cell wall 1307 is coupled to facesheet 202 along a second cell wall base edge 1308 with a third length1309. In other embodiments, not shown, core layer 200 having pluralityof first resonant cells 1201 further includes a plurality of thirdresonant cells having at least one of the same and different shapes thansecond resonant cells 1306.

FIG. 14 is an isometric partial cutaway view of a portion of yet anotheralternative embodiment of core layer 200 of acoustic liner 118 shown inFIG. 2, but depicted in a non-annular version. In this alternativeembodiment, a plurality of first resonant cells 1409 are positioned onback sheet 204 with first gap distance 702 and second gap distance 704therebetween. Each first resonant cell 1409 of plurality of firstresonant cells 1409 coupled to back sheet 204 has an equivalent firstshape. Also, in this alternative embodiment, first resonant cell 1409 isembodied in a first shape defining a right, truncated cone 1412.Truncated cone 1412 includes an annular base 1414 embodied in a circlehaving a radius and a first circumference 1415 defining first length 308(e.g., a truncated pyramid with a base having an infinite number ofsides). First resonant cell 1409 is coupled to back sheet 204 alongfirst circumference.

Also, in this alternative embodiment, first resonant cell 1409 includesa substantially planar circular frustum 1416 having a secondcircumference 1418 defining second length 312 (shown in FIG. 3) alongwhich first resonant cell 1409 is coupled to face sheet 202 at frustum1416. Second circumference 1418 is less than first circumference 1415. Adistance between annular base 1414 and frustum 1416 is approximatelyequal to thickness 207 of core layer 200. Furthermore, first shape oftruncated cone 1412-type first resonant cell 1409 contains a firstvolume 1420 therein defined by one arcuate first cell wall 1422 thereof,back sheet 204, and face sheet 202. In other embodiments, not shown,first shape of first resonant cell 1409 defines at least one of a rightnon-truncated circular cone, an oblique non-truncated circular cone, aright truncated elliptical (e.g., oblong) cone, a right non-truncatedelliptical cone, an oblique elliptical truncated cone, and an obliquenon-truncated cone.

FIG. 15 is a perspective view of the cellular structure of core layer200 shown in FIG. 14. For illustrative purposes face sheet 202 isremoved from the view illustrated in FIG. 14. As illustrated in FIG. 14,plurality of first resonant cells 1409 are positioned on back sheet 204in a spaced arrangement, where, in the axial (A) direction, adjacentfirst resonant cells 1409 are separated by first gap distance 702 andwhere, in the circumferential (C) direction, adjacent first resonantcells 1409 are separated by second gap distance 704. In this alternativeembodiment, first gap distance 702 is approximately equal to second gapdistance 704. In other embodiments, not shown, second gap distance 704is different from first gap distance 702.

In this alternative embodiment, first cell wall 1422 extends from backsheet 204 to face sheet 202 at a first angle 1502 relative to acenterline 1504 of first resonant cell 1409 drawn between a base center1506 and a frustum center 1508. A space defined by first cell wall 1422of respective truncated cone 1412-type first resonant cells 1409, backsheet 204, and face sheet 202 (e.g., at frustum 1416) contains firstvolume 1420 therein. Also, in this alternative embodiment, core layer200 of acoustic liner 118 includes a plurality of second resonant cells1510 having four second cell walls 1512. Second cell wall 1512 is formedas a trapezoidal planar sheet spanning frustum points 1514 of adjacentfrustums 1416 and two base points 1516 of adjacent annular bases 1414.Second cell wall 1512 is coupled to face sheet 202 along a second cellwall base edge 1517 with third length 1518. A sum of third lengths 1518of respective second cell walls 1512 defines a square having a thirdperimeter along which second resonant cell 1510 is coupled to face sheet202.

Second cell wall 1512 also extends from each frustum point 1514 on facesheet 202 at a second angle 1520 to a respective base point 1516 on backsheet 204. In this alternative embodiment, second cell wall 1512 iscoupled to back sheet 204 along a second cell wall top edge 1521 with afourth length 1522 less than third length 1518 and greater than 0. Thus,in this alternative embodiment, second resonant cell 1510 defines asecond shape embodied in a polyhedron having four trapezoidal facesembodied in four second cell walls 1512, and third perimeter defines asquare polygonal base having four sides, where each side has thirdlength 1518. Therefore, in this alternative embodiment, four second cellwalls 1512 of second resonant cell 1510 are coupled to face sheet 202along third perimeter. Further, in this alternative embodiment, a spacedefined by second cell walls 1512 of respective second resonant cells1510, back sheet 204, and face sheet 202 contains a second volume 1524therein.

Also, in this alternative embodiment, core layer 200 of acoustic liner118 includes a plurality of third resonant cells 1526. Third resonantcell 1526 defines a third shape (e.g., a three-dimensional shapeincluding two trapezoidal faces defined by two adjacent second cellwalls 1512 of adjacent second resonant cells 1510, and two convex facesdefined by portions of opposing first cell walls 1422 of adjacent firstresonant cells 1409 facing into third resonant cell 1526). Third shapeis further defined by four frustum points 1514 and four base points 1516of two adjacent truncated cone 1412-type first resonant cells 1409.Further, in this alternative embodiment, third resonant cell 1526 has athird volume 1528 defined by portions of two adjacent first cell walls1422, two adjacent second cell walls 1512, back sheet 204, and facesheet 202. Thus, in this alternative embodiment, a total volume of corelayer 200 in acoustic liner 118 is approximately equal to a sum of firstvolumes 1420, second volumes 1524, and third volumes 1528, of pluralityof first resonant cells 1409, plurality of second resonant cells 1510,and plurality of third resonant cells 1526, respectively.

In other embodiments, not shown, and where, for example, and withoutlimitation, first gap distance 702 is different from second gap distance704, each of first shape, second shape, and third shape have a differentshape relative to one another. In such other embodiments, plurality offirst resonant cells 1409 all have the same shape with the samedimensions. However, where first gap distance 702 is less than secondgap distance 704, second shape is embodied in an irregular, right,truncated pyramid. Similarly, as opposed to embodiments such as thoseshown and described above with reference to FIGS. 14 and 15, core layer200 of acoustic liner 118 need not have regular spacing of plurality offirst resonant cells 1409 on back sheet 204, and by extension, need nothave regular arrangements of spacing of plurality of first resonantcells 1409, second resonant cells 1510, and third resonant cells 1526.For example, and without limitation, first gap distance 702 variedrandomly in the axial (A) direction between a zero-valued distance to anon-zero-valued distance results in a random distribution of secondvolumes 1524 and third volumes 1528 in the axial (A) direction.Similarly, second gap distance 704 varied randomly in thecircumferential (C) direction between zero-valued and non-zero-valueddistances results in a random distribution of second volumes 1524 andthird volumes 1528 in the circumferential (C) direction. In still otherembodiments, not shown, dimensions of first resonant cell 1409 arevaried randomly in at least one of the axial (A) direction and thecircumferential (C) direction, resulting in random distributions offirst volumes 1420 in the respective directions, in addition to randomdistributions of second volumes 1524 and third volumes 1528. Further, instill other embodiments, not shown, shapes and/or dimensions of firstresonant cells 1409 are varied randomly in at least one of the axial (A)direction and the circumferential (C) direction, resulting in randomdistributions of first volumes 1420 in the respective directions, inaddition to random distributions of second volumes 1524 and thirdvolumes 1528.

FIG. 16 is a graphical representation, i.e., graph 1600, of operation ofcore layer 200 of acoustic liner 118. As illustrated in FIG. 16, graph1600 depicts six plots of sound absorption coefficient (a, y-axis)versus frequency in Hertz (Hz, x-axis) given a 130 decibel (dB) incidentsound pressure level (SPL) upon face sheet 202. A first plot 1602, asecond plot 1604, and a third plot 1606 represent sound absorption atthree different locations on a known single degree of freedom (SDOF)acoustic liner core layers for up to about 6500 Hz. First plot 1602,second plot 1604, and third plot 1606 share approximately equal peakabsorption coefficient values of about 0.90 at about 1500 Hz, withabsorption coefficients maintained over about 0.80 in a band offrequencies from about 1100 Hz to about 1700 Hz. Also, first plot 1602,second plot 1604, and third plot 1606 maintain absorption coefficientsover about 0.60 in a frequency band from about 700 Hz to about 2000 Hz.From 2000 Hz to 6500 Hz, absorption coefficient values of first plot1602, second plot 1604, and third plot 1606 decay exponentially at aboutthe same rates to about 0.15 at 6500 Hz.

Graph 1600 also includes a fourth plot 1608, a fifth plot 1610, and asixth plot 1612 representing sound absorption at three differentlocations on continuous degree of freedom (CDOF) acoustic liner 118having core layer 200 with truncated pyramid 302-type first resonantcells 209 substantially as shown and described with reference to FIGS. 2and 3. Fourth plot 1608, fifth plot 1610, and sixth plot 1612 attainpeak absorption coefficient values of about 1.00 at a plurality offrequencies ranging from about 800 Hz to about 3800 Hz. Also, fourthplot 1608, fifth plot 1610, and sixth plot 1612 maintain absorptioncoefficients over about 0.80 in two frequency bands from about 1000 Hzto about 2700 Hz, and from about 3300 Hz to about 3800 Hz. Furthermore,fourth plot 1608, fifth plot 1610, and sixth plot 1612 maintainabsorption coefficients over about 0.60 in a frequency band from about400 Hz to about 4400 Hz. From 4400 Hz to 6500 Hz, absorption coefficientvalues of fourth plot 1608, fifth plot 1610, and sixth plot 1612 decayexponentially at approximately the same rates to about 0.19 at 6500 Hz.Graph 1600 thus illustrates significantly wider frequency bandsextending into lower frequencies and having absorption coefficientvalues greater than 0.60 and greater than 0.80 in CDOF-based acousticliner 118 core layer 200 as compared to known SDOF acoustic liner corelayer.

FIG. 17 is a schematic diagram of noise certification points whereeffective perceived noise level (EPNL) values are determined in ameasurement scheme 1900. In measurement scheme 1900, EPNL values aretaken during operation of turbofan engine 100 having acoustic liner 118with core layer 200 including truncated pyramid 302-type first resonantcells 209 substantially as shown and described above with reference toFIGS. 2 and 3. EPNL measurements are taken at three certificationpoints. Measurement scheme 1900 includes a first certification point1902 corresponding to an airborne approach (AP) at main lobe width (MLW)of aircraft 1901 to a runway 1903 on a ground surface 1904. Firstcertification point 1902 is located on ground surface 1904 approximatelydirectly underneath and perpendicular to airborne aircraft 1901, andabout 2000 meters (m) from a touch-down point 1906 of aircraft 1901 onrunway 1903. Also, at first certification point 1902, a center-wingpoint 1908 of aircraft 1901 and touch-down point 1906 define an angle1910 approximately equal to 3 degrees relative to ground surface 1904.

Measurement scheme 1900 also includes a second certification point 1912corresponding to a sideline (SL) at maximum take-off weight (MTOW) ofaircraft 1901 after lifting-off from runway 1903. Second certificationpoint 1912 is located on ground surface 1904 about 450 m laterallyoffset from a runway point 1914 that is approximately directlyunderneath and perpendicular to center-wing point 1908 by about 1000 mafter aircraft 1901 has taken off from runway 1903. After taking-offfrom runway 1903, aircraft 1901 reaches an engine thrust reduction point1916 on a flightpath 1918 where thrust of turbofan engine 100 isdecreased and an ascent angle of flightpath 1918 is also decreasedrelative to ground surface 1904. Measurement scheme 1900 furtherincludes a third certification point 1920 corresponding to a cutback(CB) at MTOW of aircraft 1901 after take-off. Third certification point1920 is located on ground surface 1904 about 6500 m from touch-downpoint 1906 along a runway centerline 1922.

FIG. 18 is a flowchart of a method 2100 of attenuating noise from asource generating a sound wave stream. In the example embodiment, method2100 includes receiving 2102 a sound wave stream including a pluralityof frequency components at a first surface of a core layer of anacoustic structure, the core layer comprising a plurality of resonantcells occupying a thickness of the core layer. Method 2100 also includeschanneling 2104 the sound wave stream into the core layer and reflecting2106 the sound wave stream from a first surface of a first resonant cellof the plurality of resonant cells to a second surface of a secondresonant cell of the plurality of resonant cells. Method 2100 alsoincludes at least partially canceling 2108 at least some of theplurality of frequency components based on the reflecting and absorbing2110 a portion of an energy content of the reflected sound wave streamat each reflection.

FIG. 19 is a side elevation view of another embodiment of acoustic liner118 in accordance with an example embodiment of the present disclosure.In the example embodiment, additional bonding lands 2200 are formed atfrustum points along face sheet 202, such as, but not limited to, firstfrustum point 706 and second frustum point 708. Bonding lands 2200 arealso formed at corner points on back sheet 204, such as, but not limitedto, corner point 820. Bonding lands 2200 provide additional bonding areafor coupling cell wall 210 to face sheet 202 and/or back sheet 204. Theadditional bonding area includes a thickness 2202 that improves thestrength in the bonding area.

In various embodiments, cell walls 210 are formed arcuately betweenadjacent cells 209. For example, cell walls 210 may be formed concavelyor convexly with respect to any particular cell 209. In otherembodiments, cell walls 210 include baffles or surface extensions 2204that extend from a surface of cell walls 210 into cell 209. Surfaceextensions 2204 are relatively large structures rather than mere surfacetreatments. In various embodiments, surface extensions 2204 include alength 2205 that is greater than two times a thickness 2207 of cellwalls 210. In other embodiments, surface extensions 2204 include alength that is five times a thickness of cell walls 210. In still otherembodiments, surface extensions 2204 include a length that is ten timesa thickness of cell walls 210. Surface extensions 2204 may extend fromcell walls 210 at a right angle 2206 or at a non-orthogonal angle 2208.Surface extensions 2204 are sized and positioned along cell wall 210 tomaximize a reflection of acoustic energy within cell 209 and improveresonance within cells 209. Although, as illustrated as having a singlesurface extension 2204 on each cell wall 210, any number of surfaceextensions may be spaced along cell wall 210. Moreover, a spacingbetween surface extensions 2204 on any cell wall 210 may be uniform ornon-uniform.

FIG. 20 is a side elevation view of acoustic liner 118 in accordancewith another example embodiment of the present disclosure. In theexample embodiment, acoustic liner 118 has an annular construction andis disposed along duct inner wall 112 (shown in FIG. 1). A thickness2300 of acoustic liner 118 varies along a length of acoustic liner 118.In an exemplary embodiment, acoustic liner 118 is formed as anon-cylindrical acoustic liner 118 and is positioned along duct innerwall 112 extending from a position upstream 2301 of fan blades 106 to aposition downstream of fan blades 106, and/or along non-rotatingportions of nacelle 102 (shown in FIG. 1) or other components, ducts, orcasings within turbofan engine 100 (shown in FIG. 1) where noisesuppression (e.g., attenuation) is appropriate, or which are capable ofintercepting and suppressing noise having a predetermined range offrequencies. In the example embodiment, a plurality of acoustic cells2302 are formed by a plurality of cell walls 2304, which are similar tocell walls 210 (shown in FIG. 2). Cell walls 2304 extend between a facesheet 2306 and a back sheet 2308, which are similar to face sheet 202and back sheet 204 (shown in FIG. 2). In various embodiments, cell walls2304 form equal angles 2310 at each joint 2312 between adjacent cellwalls 2304 and face sheet 2306. In other embodiments, acoustic cells2302 are spaced evenly apart in that a distance 2314 between joints 2312are approximately equal.

It is understood from the foregoing description and associated figuresthat the generally pyramidal shape of the first resonant cells on corelayer is presented by way of example, and not in a limiting sense. Othersound wave absorptive properties and acoustic operationalcharacteristics may be achieved using further variations on orientationsof first resonant cells in acoustic liner core layers including, withoutlimitation, positioning of second, third, and/or fourth resonant cellsin core layers in relation to the first resonant cells. Such otherembodiments utilized for core layers of acoustic liners and acousticstructures not having face sheets and back sheets still fall within thescope of the CDOF acoustic liners described herein for realizingacoustic suppression of greater numbers of frequencies relative to knownSDOF and two degree of freedom (2DOF) core layers. Further, theabove-described structures, systems and methods are not limited to thespecific embodiments described herein, but rather, components of systemsor steps of the methods may be utilized independently and separatelyfrom other components or steps described herein. For example, theacoustic structures having the above-described core layers may also beused in applications other than vehicle and other engines whereCDOF-based acoustic structures are desirable for noise suppression(e.g., noise damping) in a number of environments, and in combinationwith any number of other sound wave absorption systems and methods.

Additionally, it should be understood that a foam material may be usedwithin or surrounding the cells of acoustic liner 118. Such foammaterial may facilitate the acoustic performance of acoustic liner 118and or the structural strength of acoustic liner 118.

Although specific features of various embodiments of the disclosure maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the disclosure, any featureof a drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

What is claimed is:
 1. An acoustic liner comprising: a face sheet; aback sheet spaced from said face sheet; and a core layer comprising: aplurality of adjacent cavities extending between said face sheet andsaid back sheet; a thickness defined by a distance between said facesheet and said back sheet, said core layer further comprising: aplurality of first resonant cells, each first resonant cell of saidplurality of first resonant cells comprising: at least one first cellwall coupled to said back sheet along a first cell wall base edge, saidat least one cell wall extending from said back sheet at a first angletoward said face sheet, said at least one first cell wall furthercoupled to said face sheet along a first cell wall top edge, said firstresonant cell formed in a first shape, said first resonant cellcontaining a first volume in a space defined by said at least one firstcell wall, said back sheet, and said face sheet, said first cell wallbase edge comprising a first length, and said first cell wall top edgecomprising a second length, said second length less than said firstlength.
 2. The acoustic liner of claim 1, wherein said plurality offirst resonant cells are positioned on said back sheet in a gridarrangement.
 3. The acoustic liner of claim 1, wherein said plurality offirst resonant cells are positioned on said back sheet in an offsetarrangement.
 4. The acoustic liner of claim 1, wherein the second lengthis approximately equal to zero.
 5. The acoustic liner of claim 1,wherein said back sheet, said face sheet, and said core layer are formedas at least one of: a substantially flat acoustic liner; an arcuatecylindrical acoustic liner; a complexly curved acoustic liner.
 6. Theacoustic liner of claim 1, wherein said first length defines a firstperimeter and said first shape defines a pyramid, said at least onefirst cell wall comprising at least three faces of said pyramid, saideach first resonant cell further comprising a first polygonal basehaving at least three sides and said first perimeter, said at least onefirst cell wall further coupled to said back sheet along said firstperimeter.
 7. The acoustic liner of claim 6, wherein said first shapefurther defines at least one of a right pyramid, an oblique pyramid, aregular pyramid, and an irregular pyramid.
 8. The acoustic liner ofclaim 6, wherein said first shape further defines a truncated pyramidcomprising a frustum, and wherein said second length is defined by asecond perimeter of said frustum, said at least one first cell wallfurther coupled to said face sheet along said second perimeter.
 9. Theacoustic liner of claim 1, wherein said first length defines a firstcircumference and said first shape defines a cone, said each firstresonant cell further comprising an annular base having said firstcircumference, said at least one first cell wall coupled to said backsheet along said first circumference.
 10. The acoustic liner of claim 9,wherein said first shape further defines at least one of a rightcircular cone, an oblique circular cone, a right elliptical cone, and anoblique elliptical cone.
 11. The acoustic liner of claim 9, wherein saidfirst shape further defines a truncated cone comprising an annularfrustum, and wherein said second length is defined by a secondcircumference of said annular frustum, said at least one first cell wallcoupled to said face sheet along said second circumference.
 12. Theacoustic liner of claim 1, said core layer further comprising aplurality of second resonant cells, each second resonant cell of saidplurality of second resonant cells comprising: at least two second cellwalls, each second cell wall of said at least two second cell wallscoupled to said face sheet along a second cell wall base edge, said eachsecond cell wall extending from said face sheet at a second angle towardsaid back sheet, said each second cell wall further coupled to said backsheet along a second cell wall top edge, said each second resonant cellformed in a second shape, said each second resonant cell containing asecond volume in a space defined by said at least two second cell walls,said back sheet, said face sheet, and at least two adjacent firstresonant cells of said plurality of first resonant cells, said secondcell wall base edge comprises a third length, and said second cell walltop edge comprising a fourth length, said fourth length is less thansaid third length.
 13. The acoustic liner of claim 12, wherein saidthird length defines a third perimeter and said second shape defines apolyhedron, said at least two second cell walls comprising at leastthree faces of said polyhedron, said each second resonant cell furthercomprising a second polygonal base having at least three sides and saidthird perimeter, said at least one second cell wall further coupled tosaid face sheet along said third perimeter.
 14. The acoustic liner ofclaim 12, wherein said second shape defines at least one of a regularpolyhedron and an irregular polyhedron.
 15. The acoustic liner of claim12, said core layer further comprising a plurality of third resonantcells, each third resonant cell of said plurality of third resonantcells formed in a third shape, said each third resonant cell containinga third volume in a space defined by at least two second cell walls,said back sheet, said face sheet, and said at least two adjacent firstresonant cells.
 16. The acoustic liner of claim 15, wherein each of saidfirst shape, said second shape, and said third shape have a differentshape relative to one another.
 17. The acoustic liner of claim 15,wherein said first shape and said third shape alternate in an axialdirection, the axial direction substantially perpendicular to acircumferential direction.
 18. The acoustic liner of claim 15, whereinsaid first shape and said third shape alternate in a circumferentialdirection, the circumferential direction substantially perpendicular toan axial direction.
 19. The acoustic liner of claim 15, wherein saidthird shape defines at least one of a regular non-pyramidal polyhedron,an irregular non-pyramidal polyhedron, a right pyramid, an obliquepyramid, a regular pyramid, and an irregular pyramid.
 20. An acousticstructure comprising: a core layer comprising: an inner side and anouter side spaced opposite said inner side across a thickness definedtherebetween; and a plurality of first resonant cells occupying thethickness of said core layer, each first resonant cell of said pluralityof first resonant cells comprising: at least one first cell wallextending at a first angle from a first cell wall base edge along theouter side to a first cell wall top edge along the inner side, saidfirst resonant cell formed in a first shape, said first resonant cellcontaining a first volume in a space defined by said at least one cellwall, the inner side, and the outer side, said first cell wall base edgecomprising a first length, and said first cell wall top edge comprisinga second length, said second length less than said first length.
 21. Amethod of attenuating noise from a source generating a sound wavestream, said method comprising: receiving a sound wave stream includinga plurality of frequency components at a first surface of a core layerof an acoustic structure, the core layer comprising a plurality ofresonant cells occupying a thickness of the core layer; channeling thesound wave stream into the core layer; reflecting the sound wave streamfrom a first surface of a first resonant cell of the plurality ofresonant cells to a second surface of a second resonant cell of theplurality of resonant cells; at least partially canceling at least someof the plurality of frequency components based on the reflecting; andabsorbing a portion of an energy content of the reflected sound wavestream at each reflection.
 22. An acoustic liner comprising: a facesheet comprising a plurality of bonding lands; a back sheet comprising aplurality of bonding lands and spaced from said face sheet; and a corelayer sandwiched between said face sheet and said back sheet, said corelayer comprising a plurality of cell walls extending between arespective face sheet bonding land to a respective back sheet bondingland to form said plurality of adjacent resonant cells.
 23. The acousticliner of claim 22 wherein at least some of said plurality of cell wallsextend arcuately between said face sheet and said back sheet to form theplurality of adjacent resonant cells.
 24. The acoustic liner of claim 22wherein at least some of said plurality of cell walls comprise at leastone surface extension.
 25. The acoustic liner of claim 24 wherein atleast some of said plurality of cell walls comprise at least one surfaceextension extending from a surface of a respective cell wall of the atleast some of said plurality of cell walls into an adjacent resonantcell.
 26. The acoustic liner of claim 22, wherein at least two cellwalls of the plurality of cell walls connect to each single bonding landforming an angle between the at least two cell walls and wherein aplurality of the formed angles are equal with respect to each other. 27.The acoustic liner of claim 22, wherein an apex of the formed angles areuniformly spaced with respect to each other.
 28. The acoustic liner ofclaim 1, wherein at least one of said plurality of adjacent cavities andsaid plurality of first resonant cells are at least partially filledwith a foam material.